This invention relates generally to improvements in water purification systems and equipment of the reverse osmosis type. More particularly, this invention relates to an improved filter cartridge for a reverse osmosis purification unit, wherein multiple filter stages are integrated into a compact and unitary cartridge form adapted for simplified installation and replacement on an as needed periodic basis.
Reverse osmosis water purification systems are, in general terms, relatively well known in the art for producing a relatively purified water supply used for drinking, cooking, etc. Such purification systems commonly include a reverse osmosis unit having a reverse osmosis membrane which, in the presence of appropriate flow and pressure conditions, separates an incoming tap or feed water supply into the purified water supply and a relatively impure or reject water supply. In particular, the membrane functions to remove particulate matter and a wide range of dissolved solids and other contaminants from a portion of the feed water to produce the purified water supply, and to concentrate those contaminants within the remainder of the feed water thereby producing the reject supply, sometimes referred to as brine, for disposal via a suitable drain. The purified water supply is normally collected for storage at a convenient location within a suitable reservoir, and for ready dispensing through a faucet valve or the like when desired. In this regard, available reverse osmosis systems may be designed to utilize compressed air to deliver purified water from the reservoir as described, for example, in U.S. Pat. No. 4,834,873. Alternately, the system may be designed to use the pressure of the feed water to deliver purified water from the reservoir as described, for example, in U.S. Pat. No. 4,776,952.
Reverse osmosis membranes have been constructed from different materials which are known to provide different performance efficiency and rate of production of purified water. However, in many reverse osmosis systems, the choice of membrane material is dictated not by performance efficiency but instead by the chemical or bacteriological makeup of the feed water in a local water supply. For example, so-called thin film or thin film composite membranes are generally preferred in view of relatively high operational efficiencies which can be obtained from highly compact membrane cartridges having a large membrane surface area, substantially without degradation in the presence of certain bacterial organisms present in some feed water supplies. However, such thin film membranes are known to degrade rapidly in the presence of certain chemicals, particularly oxidants such as chlorine and/or compounds thereof which are often added to a local water supply to retard growth of bacteria and other organisms. Accordingly, when chlorine is present in the feed water supply, alternative and less efficient membrane materials such as cellulose acetate have normally been used to provide acceptable membrane operating life, but with an acknowledged reduction in pure water production rate and a relatively high susceptibility to bacterial attack. Alternatively, in some systems, carbon prefilters or the like have been used upstream of a thin film membrane to remove chlorine from the feed water supply prior to reverse osmosis processing. While this latter approach can prevent premature failure of the thin film membrane, it has also required additional filter housing and filter element structures to increase the overall size and cost of a reverse osmosis system.
The present invention overcomes the problems and disadvantages associated with the prior art by providing an improved filter cartridge for a reverse osmosis system, wherein the filter cartridge includes a compact membrane of the thin film type in combination with a prefilter stage which protects the membrane against contact with otherwise harmful constituents within the local water supply.